Abrasive blast modification of surfaces

ABSTRACT

A metal surface treatment method wherein the surface ( 10 ) is simultaneously bombarded with a mixture of abrasive particles ( 4 ) and dopant particles ( 6 ) which are delivered at a velocity in the range of 50-250 m/sec, and thereby depositing the dopant material on the surface. Also provided is an article ( 8 ) having a surface treated by such a method.

FIELD OF THE INVENTION

The present invention relates to surface treatment techniques in thefield of materials science.

BACKGROUND TO THE INVENTION

Metal surface finish is often provided using particle bombardment. Thiscan vary from material removal using abrasive blasting through tomaterial deposition using cold spraying. The difference in theseapproaches rests in the energy of the processes. Despite its name, thecold spray process actually uses elevated temperatures. The gas used tocarry the particles is heated to a temperature of several hundreddegrees, typically between 200° C. and 1000° C., before it is mixed withthe bombardment particles. This increases the gas velocity withoutincreasing the line pressure feeding the gas. Typically cold sprayprocesses operate at elevated temperatures but below the melting pointof the metallic bombardment particles that are employed. In addition tothe thermal energy provided by the heated gas, the kinetic energy of thebombarding particles is also higher in cold spray systems as theparticles travel at significantly higher velocities than in abrasiveblasting. The particles are typically accelerated to supersonic speeds(greater than 342 m/sec). At high velocities, greater than 300 m/sec,the energy imparted by the impact of the particle against the surfacecan be sufficient to cause both the metal surface and the bombardingmetal particle to deform and the resultant interaction causes theparticle to spread out and coat the surface. The minimum velocityrequired to achieve this coating deposition is referred to as the‘critical velocity’ in cold spray technology. Due to the requirement forthe bombarding particle to deform upon impact, there has been limitedapplicability of this technology to the deposition of non-metallicmaterials. At values below the critical velocity, very littleimpregnation of the surface occurs and the bombarding particlestypically bounce off the surface. The widely quoted minimum criticalvelocity for a wide range of materials is 400 m/sec, as outlined inGrigoriev et al. (Surf. Coat. Technol., 268 (2015), pg 77-84) and asshown in the present FIG. 1, which is taken from that publication. Thisvalue can vary depending upon the bombarding particles and theproperties of the substrate surface.

In most metallic materials an oxide layer forms at the surface, whichwill be harder than the bulk metal or alloy. Metal surfaces (especiallythose of titanium and titanium derived alloy) are naturally contaminatedin air by a variety of contaminants. The detailed physical and chemicalproperties of any metal surface depend on the conditions under whichthey are formed. The inherent reactivity of the metal can also attractvarious environmental chemicals/contaminants that oxidize on thesurface. For example, titanium is a highly reactive metal, which isreadily oxidized by several different media. This results in titanium,and most other metals, always being covered in an oxide layer. Thisoxide layer is chemically stable and much harder than the bulk metalunderneath. As the metal oxide is typically much harder and lessreactive than the metal, the ability of the bombarding particles to bondto the substrate is often limited by the properties of the oxide and notby the properties of the underlying metal.

This is also true of cold spray technologies, which are also limited bythe properties of the surface that can be treated. In order for the coldspray coating to adhere, the substrate surface must be cleaned androughened. This is often accomplished by abrasively blasting the surfacebefore cold spraying. In some instances, cold spray coatings have beenundertaken which also incorporate some abrasive particles alongside themetal dopant, but these have all been deposited at high velocities andat elevated temperatures beyond the range of abrasive blasting.Experimentally, it has been found that the presence of the ceramicparticles acts to increase the deposition rate of the metal. Inaddition, the presence of the ceramic may enhance the wear resistance ofthe deposit.

Most surface bombardment processes are not focussed on materialdeposition, but rather on surface roughness and stress. If roundparticles are used to bombard the surface and the velocity is lowenough, at subsonic speeds that are below the critical velocity, thenthe surface is merely deformed and dimpled by the bombardment. This isreferred to as shot peening and it is routinely used to control surfacestress by applying compressive stress to the surface, and this processleaves a characteristic dimpled surface appearance.

If particles with an angular or irregular morphology are used to bombardthe surface at values below the critical velocity, then the edges andcorners of the bombarding particles can cut up and erode material fromthe substrate metal. This results in abrasion of the surface, andabrasive blasting is widely used to clean and roughen metal surfaces.For optimum abrasive effects, the abrasive particles are chosen to havea Mohs hardness of at least 5, though harder particles are preferred asthe abrasion increases with hardness.

During the abrasive blasting process, it has been observed that someparticles of abrasive are left impregnated in the substrate. For manyapplications, this is considered a detrimental effect and furtheretching or cleaning steps are required to remove the contamination.However, there are applications where the contamination arising fromabrasive blasting has been postulated to be beneficial. U.S. Pat. No.4,194,929 describes a process wherein a stainless steel surface isblasted with iron or steel abrasive. As ferrous particles are embeddedin the corrosion resistant steel surface, this causes a passivatingcoating to form in a conventional zo phosphating solution. In U.S. Pat.No. 7,377,943, Müller et al. describe a process for improving thebioactivity of a metal surface by blasting the surface with a powderwherein each particle comprises a vitreous crystalline material madefrom a combination of CaO, P₂O₅, ZrO₂ and fluoride. The resultantparticles are embedded in the surface to improve the biocompatibility ofthe metal surface. These methods all involve bombarding the surface witha single type of particle and feature a combination of abrasion andimpregnation.

In a further development of this, Ishikawa et al. (J. Biomed. Mat. Res.(Appl. Biomat.), vol. 38, pg. 129-134, 1997) reported on the blasting oftitanium with a hydroxyapatite powder using conventional abrasiveblasting equipment. They observed that the powder built up on the metalsurface without any evidence of substrate abrasion when examined usingelectron microscopy. They attributed this coating formation to thereactivity of the hydroxyapatite material which resulted in a form ofparticle sintering and to some adhesion to the surface. Although stableto ultrasonic washing, the coating was removed by scratching with asteel blade, indicating only moderate coating adhesion was achieved.This suggests minimal bonding of the bombarding particles to the metaland microscopy seems to confirm this, with no evidence of metal abrasionevident.

This may be due to the hard passive oxide layer that is present ontitanium. The soft hydroxyapatite particles would therefore not beexpected to rupture and abrade the metal oxide.

Others have sought to deposit materials on the surface of a metal usinga combination of two sets of particles which are dissimilar. U.S. Pat.No. 3,754,976 describes a process for metal plating. While cold sprayuses high velocity bombardment to adhere a metal to a surface, thispatent disclosed a process for metal plating in which a mixture ofmetallic powder and small shot peening particles are sprayed against asurface at a velocity sufficient to impact and bond the metallic powderonto the surface. The peening particles effectively deform and plate themetal particles onto the surface without any significant uptake ofpeening particles in the coating. This technique was later expanded toinclude additional materials that could be deposited. U.S. Pat. No.4,552,784 describes a process for depositing rapidly solidified metalpowder using this technique. U.S. Pat. No. 4,753,094 claims a processwherein a combination of molybdenum disulphide and round metal shot wasblasted at a surface to deposit a layer of molybdenum disulphide. US2006/0089270 claims a process wherein shot peening particles are mixedwith a primary lubricant such as molybdenum disulphide and a polymericlubricant such as polytetrafluoroethylene (PTFE) and blasted at asurface to deposit a mixture of the two lubricants on the surface. Inall of these dual blasting methods, the inventors chose to use shotpeening particles to bombard the surface alongside the coating materialas the spherical shot peen particles would not abrade the coating as itdeposited. Convention dictated that blasting with a combination ofabrasive particles and a coating precursor would not produce a depositedcoating as the abrasive would have been expected to remove any coatingthat formed.

In order to combine roughening of an abrasive blast process and adeposition process in a single step, others have looked at complexstratified particles in which an abrasive is covered with the coatingforming material. The Rocatec™ system for the silicization of metallicand other surfaces uses individual particles having multiple components.This technology is used extensively in the dental arena. In thisinstance an alumina particle having an outer adherent layer of silica ispropelled at a pre-roughened surface and upon impact the local heatgenerated in the vicinity of the impact causes the shattered silicaouter layer to become fused to the surface through a process referred toas ceramicization. Similar strategies are outlined U.S. Pat. No.6,468,658 and U.S. Pat. No. 6,431,958 in which abrasive particles arecoated with a material and then blasted at a surface in order to embedthe outer layer in the surface. In all of these cases, the abrasive iscontained within an outer shell and therefore abrasion is limited andthe surface is chemically modified. However these techniques all requirethe use of complex coated media which is expensive to produce, and thiswas deemed necessary as simply blasting with a simple mix of abrasiveparticles and coating material was not considered due to the expectedremoval of the coating by the abrasive action.

Despite this widespread belief, it was discovered by O'Donoghue et al.(EP 2061629 and U.S. Pat. No. 8,119,183) that a combination of abrasivesand coating materials could prove beneficial. Previous mixed mediacoatings had focussed on the use of round shot peen media that merelydeposited the precursor powder as a laminate layer on top of the passiveoxide that covered the metal. These laminate layers were prone to pooradhesion and could delaminate. By grit blasting the surface with acombination of abrasive and dopant, it was found that the abrasiveremoved the passive oxide layer and roughened the surface. With the hardpassive oxide layer removed and a reactive layer of metal exposed, thisfacilitated impregnation of the dopant into the metal. This did notproduce a laminate layer and ensured excellent adhesion of the dopant tothe substrate, and this technique has been commercialised under thetrade name CoBlast. Due to the tendency of metal dopants to deform andspread rather than shattering and embedding into the surface, the methodis better suited to the deposition of non-metallic dopants.

While blasting a mixture of abrasive and dopants at a surface using theestablished CoBlast technique was effective at depositing materials intothe substrate (and indeed there is no question that EP 2061629 (andrelated patents) discloses its invention in a manner sufficiently clearand complete for it to be carried out by a person skilled in the art)the optimum process parameters for CoBlast were not well understood. Inparticular, the critical particle delivery velocity required toimpregnate the surface with a dopant was not well established, andsub-optimal coatings could therefore result.

There has therefore been a desire to improve the CoBlast techniquethrough improved identification of process parameters, in particular inrespect of the particle delivery velocity.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention there is provided ametal surface treatment method wherein the surface is simultaneouslybombarded with a mixture of abrasive particles and dopant particleswhich are delivered at a velocity in the range of 50-250 m/sec (metresper second), and thereby depositing the dopant material on the surface.

For instance, the particles may be delivered at a velocity in the rangeof 100-200 m/sec, for example at a velocity in the range of 120-180m/sec.

The method may be carried out at ambient temperature.

Preferably the abrasive particles have an irregular or angularmorphology.

The dopant may be directly chemically bonded to the metal surfacewithout any intermediate oxide layer. Alternatively, or in addition, thedopant particles may be agglomerated together on the metal surface.

Preferably the abrasive has a hardness greater than 6.0 on the Mohsscale. For example the abrasive may have a hardness of 8.0 or above onthe Mohs scale.

Preferably the abrasive has a hardness at least 2 levels higher thanthat of the dopant on the Mohs scale. Particularly preferably theabrasive has a hardness at least 3 levels higher than that of the dopanton the Mohs scale.

In certain embodiments the dopant may be a polymer or other low densitymaterial (having a density of less than 2.5 g/cm³) and the abrasive mayhave an average particle size in the range of 150-1500 microns (μm). Forexample, the abrasive may have an average particle size in the range of250-1000 microns, such as in the range of 350-750 microns. As a furtherexample, the abrasive may have an average particle size of greater than300 microns.

In other embodiments the dopant may be a polymer (or alternatively maybe a non-polymer), and the abrasive may have an average particle size inthe range of 5-5000 microns, such as in the range of 5-1500 microns. Forexample, the dopant may be a polymer and the abrasive may have anaverage particle size in the range of 10-150 microns. Merely as twoillustrative examples, we have achieved good deposition of polymerdopants using abrasive particles having an average particle size of 13microns and, separately, using abrasive particles having an averageparticle size of 50 microns. The variation in abrasive size is typicallyassociated with the desired texture required on the finished surface.

With the dopant being a polymer, the abrasive may constitute at least 60wt % of the mixture of abrasive and dopant particles. Preferably theabrasive constitutes at least 70 wt % of the mixture of abrasive anddopant particles. More preferably the abrasive constitutes at least 80wt % of the mixture of abrasive and dopant particles.

In other embodiments the dopant may be a non-polymeric material and theabrasive may have an average particle size of less than 500 microns. Forexample, the abrasive may have an average particle size of less than 200microns, or less than 150 microns. With the dopant being a non-polymericmaterial, the dopant may constitute at least 20 wt % of the mixture ofabrasive and dopant particles. Preferably the dopant constitutes atleast 25 wt % of the mixture of abrasive and dopant particles. Morepreferably the dopant constitutes at least 40 wt % of the mixture ofabrasive and dopant particles.

More generally, the dopant particles may have an average particle sizein the range of 1-100 microns.

Typically less than 10 microns of dopant material are deposited on thesurface.

At least some of the dopant particles may penetrate the metal surfaceand remain physically impregnated in the metal.

Depending on the application, one or more additional coatings maysubsequently be applied on top of the deposited dopant material. Forexample, an additional coating may be applied through a bombardmenttechnique selected from cold spray, peen plating or microblasting. Otherways of applying an additional coating are also possible, such as powdercoating or painting.

According to a second aspect of the present invention there is providedan article having a surface treated by a method in accordance with thefirst aspect of the invention.

According to various embodiments of the first and second aspects of theinvention, the surface that is treated may be at least a part of:

-   -   an implantable medical device;    -   a marine or land-based vehicle;    -   an aerospace vehicle, satellite, rocket or spacecraft;    -   an electronic device or component;    -   a mould; or    -   a pipe, tube or storage vessel.

Other applications are also possible, as those skilled in the art willappreciate.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described, by way of exampleonly, and with reference to the drawings in which:

FIG. 1 illustrates the classification of thermal spray processes inaccordance with particle velocity and flame temperature (from Grigorievet al.);

FIGS. 2a, 2b and 2c schematically illustrate a process for treating ametal substrate;

FIGS. 3a, 3b and 3c are schematic diagrams of three different nozzleconfigurations to deliver abrasive particles and dopant particles to asurface;

FIG. 4 shows optical micrographs of a 12 micron thick nickel layerelectrolytically plated onto aluminium, (A) untreated and (B) followinga CoBlast treatment to deposit calcium phosphate;

FIG. 5 shows EDX analysis of the untreated nickel plate of FIG. 4(A) andof the calcium phosphate surface of FIG. 4(B) deposited onto the nickelplate (the calcium phosphate example being referred to as “Solar Black”in FIG. 5); and

FIG. 6 shows optical micrographs of a superelastic NiTi wire onto whichpolytetrafluoroethylene (PTFE) had been deposited (a) without the use ofabrasive particles, (b) by a CoBlast treatment using <50 μm aluminaabrasive particles, and (c) by a CoBlast treatment using <90 μm aluminaabrasive particles, in each case before and after flexural testing ofthe wire.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present embodiments represent the best ways known to the applicantsof putting the invention into practice. However, they are not the onlyways in which this can be achieved.

Overview of CoBlast method

For the general details of the CoBlast method, the reader is initiallyreferred to WO 2008/033867, which describes techniques for thesubstantially simultaneous deposition of first and second sets ofparticles. Naturally, as those skilled in the art will appreciate, thefirst and second sets of particles are different from one another. Thatis to say, the dopant species is different from the abrasive.

Embodiments of the CoBlast method are encompassed in but not limited tothe schematic representation shown in FIGS. 2a, 2b and 2 c.

FIG. 2a schematically shows a fluid jet (nozzle) 2 that delivers astream 3 comprising a set of abrasive particles 4 substantiallysimultaneously with a set of dopant particles 6. Particle sets 4 and 6bombard a surface 10 of a metal substrate 8, to impregnate the surfaceof the metal substrate with the dopant.

In the schematic representation of FIGS. 2a, 2b and 2c , the surface 10is a metal oxide layer. As a result of bombardment by the abrasiveparticles 4, the surface oxide layer is disrupted, and breaches in theoxide layer 10 result to expose a new surface 10 a of substrate 8 (FIG.2b ). In the case of a metal substrate, the newly exposed surface is ametal surface. As the particle stream 3 continues to impinge thesubstrate 8, the dopant particles 6 are integrated into the surface 10of the substrate 8 (FIG. 2c ).

In some embodiments, the blasting equipment can be used in conjunctionwith controlled motion such as CNC (computer numerical control) orrobotic control. Either the blast nozzle, the substrate or both may bemanipulated so as to achieve the desired surface treatment. The blastingcan be performed in an inert environment. The use of an inert atmosphereis typically required to manage explosion or flammability risksassociated with dopant or substrate materials and is not a specificrequirement in forming a coating.

In one embodiment, the dopant and abrasive particles are contained inthe same reservoir and are delivered to a surface from the same jet(nozzle). In another embodiment, the dopant particles are contained inone reservoir and the abrasive particles are contained in a separatereservoir, and multiple nozzles deliver the dopant and abrasiveparticles. The multiple nozzles can take the form of a jet within a jet,i.e., the particles from each jet bombard the surface at the sameincident angle. In another embodiment, the multiple nozzles arespatially separated so as to bombard the surface at different incidentangles yet hit the same spot on the surface simultaneously.

FIGS. 3a, 3b and 3c are schematic diagrams of three different nozzleconfigurations to deliver the dopant and abrasive particles to asurface: single nozzle (FIG. 3a ); multiple nozzles with dopant andabrasive particles delivered from separate reservoirs where one nozzleis situated within another nozzle (FIG. 3b ); and multiple, separatenozzles with dopant and abrasive particles delivered from separatereservoirs (FIG. 3c ). More specifically, FIG. 3a shows a single nozzle20 for delivering a single stream 23 of abrasive particles 24 and dopantparticles 26 to a substrate 28. FIG. 3b shows that multiple nozzles withdopant and abrasive particles delivered from separate reservoirs can beused, with FIG. 3b illustrating one nozzle 30 for delivering a stream 33of abrasive particles 24 situated within another nozzle 40 fordelivering a stream 43 of dopant particles 26, where streams 33 and 43are coaxial. Multiple, separate nozzles with dopant and abrasiveparticles delivered from separate reservoirs can also be used, asindicated in FIG. 3c , which shows nozzles 30 and 40, for deliveringstreams 33 and 43 of abrasive particles 24 and dopant particles 26,respectively.

The distance D between the nozzle(s) and the substrate surface can be inthe range of 0.1 mm to 250 mm, such as a range of 0.1 mm to 130 mm, or arange of 5 mm to 50 mm. The angle of the nozzle to the surface can rangefrom 10 degrees to 90 degrees, such as a range of 30 degrees to 90degrees, or a range of 70 to 90 degrees.

More than one type of dopant species can be used. It will readily beappreciated that where more than one type of dopant is used, the dopantsmay be delivered from a single nozzle, or each type may respectively bedelivered from a separate nozzle.

More than one type or size of abrasive can be used. This may beundertaken to both assist in the deposition of dopant material and alsoto customise the surface topography and level of texturing duringprocessing. It will readily be appreciated that where more than one typeof abrasive is used, the abrasives may be delivered from a singlenozzle, or each type may respectively be delivered from a separatenozzle.

Optimised CoBlast method

Although higher particle velocities are known to assist with deposition,these require increased gas pressures or temperature and this increasesthe cost of the process. Therefore, an optimised coating can result frompremixing an angular abrasive with a particulate dopant, and deliveringthe powder mix to a metal substrate surface at a velocity of 50-250m/sec, so as to remove the oxide layer from the surface, andsimultaneously depositing less than 10 microns of dopant on the surface.At least a portion of the deposited materials penetrate the metalsurface and remain impregnated within the metal. This process alsoresults in direct chemical bonding of the dopant to the surface, withoutthe presence of any intermediate oxide layer. In a preferred embodiment,the mixture of abrasive and dopant particles is delivered at a velocityof 100-200 m/sec to the surface. Optimally, the particles are deliveredat a velocity of 120-180 m/sec. If the dopant particles are delivered ata different velocity than the abrasive particles, then it has been foundthat the velocity of the abrasive particles dominates the effect at thesurface, and therefore it is the abrasive that has to be delivered atthe correct velocity.

To achieve optimal impregnation of the dopant into the surface, anangular abrasive particle with a hardness greater than 6.0 on the Mohsscale is required.

Using a harder abrasive can increase the deposition rate and an abrasivewith a hardness of 8.0 or above is preferred. Using an abrasive such asthis is sufficient to remove the oxide layer from a metal even at lowvelocity. In addition, the abrasive cleans the surface and ensures thatno complex cleaning or roughening of the surface is needed prior todeposition. However, when mixed with a dopant delivered at a velocity of100-200 m/sec, it has been found that the abrasive removes the oxide andalso erodes some of the metal underneath. Due to the simultaneousabrasion and dopant delivery, several microns of dopant are depositedand this replaces the lost metal and metal oxide, and the cumulativeeffect is that the overall thickness of the substrate remains similar tothat of the starting material. When using an angular or irregularlyshaped abrasive with a Mohs hardness greater than 6.0 and a velocity of100-150 m/sec, it has been found that less than 5-10 microns is removedby abrasion and this can be largely replaced by the dopant deposition.

The impact of the abrasive also acts to roughen and twist the metalsurface, thereby embedding and interlocking the dopant into the surface.In order to maximise deposition of the dopant, the Mohs hardness of theabrasive is preferably chosen to be at least 2 levels higher than thatof the dopant. This ensures preferential uptake of the dopant andminimal impregnation of the abrasive into the surface. Particularlypreferably, the abrasive is at least 3 levels harder than the dopant onthe Mohs scale.

The dopant is found to be chemically bonded to the surface. Given thatthe reaction happens in ambient atmosphere, it is surprising that thereis no evidence of oxide layers between the dopant and the metal.Instead, the dopant is bonded directly to the reactive metal. Thisensures excellent adhesion of the dopant to the zo metal. In addition,the dopant particles are shattered and torn by the impact on the surfaceand the ongoing abrasive action of the abrasive particle bombardment.For crystalline or semi-crystalline dopant powders, this can producenano-crystalline dopant particles on the surface, and the resultant highsurface energy and reactivity of these sub-micron particles results inmaterials that bond readily with the metal and which also agglomerateand fuse together on the surface.

Due to the reactivity induced by the abrasion, high velocities, similarto those found in cold spray, are not required. In addition, the processcan occur at ambient temperature and neither the substrate nor the gasstream need be heated as in cold spray. All of the reactions occur atless than 100° C. Although there is no direct heating and it is a roomtemperature process, the localised heating induced by the kinetic energyof the impact of the particles may be important in localised reactions.For example, during the deposition of polymeric dopants, the localisedreactions may give rise to T_(G) modification of the polymer material.

Although carried out at low temperatures, the bombardment of the surfacedoes alter the structure of the substrate. Without being bound bytheory, aside from the erosion of surface material by the process,microscopic analysis has shown that the abrasive alters the structure ofthe metal substrate, switching it from coarse grains to fine grains,thereby making it more reactive. The formation of nano-crystallinityalso occurs on the substrate side of the interface. Blasting induces alevel of Severe Plastic Deformation (SPD) on the substrate and thebombardment thereby increases the dislocation density at the newlyexposed surface, which increases the numbers of ultra-fine grains andtherefore the overall density of grain boundaries. Grain boundariesprovide reaction sites and thus increase the reactivity of a surface.This increase in grain boundary availability increases the reactivity ofthe metal interface to a depth of 20 μm. When combined with the energytransferred from the impacting abrasives and the removal of thepassivating oxide layer, this work hardening of the metal could also beexpected to enhance the bonding of the dopant to the substrate. Inaddition, there is no heat affected zone as would be expected from ahigh energy plasma spray or hot zo deposition process. This combinationof effects gives rise to direct chemical bonding of the dopant to thesubstrate. In the case of ceramic dopants, this can give rise to adiffusion bonded material. The work hardening also improves the fatiguelife of the metal substrate when compared to untreated components.

The localised reactions also allow for materials to be deposited in anadherent manner which do not normally stick. For example, materials suchas PTFE are routinely used as non-stick surfaces as it is notoriouslydifficult to make PTFE adhere to anything. Despite this, it is possibleto deposit an adherent PTFE deposit by mixing PTFE with an angularabrasive and blasting it at a surface. Without being bound by theory, itis possible that the abrasive actually shreds the polymer chain andleaves dangling, unreacted chemical bonds where the chain was cut. Thosewould provide very reactive sites that could bind to reactive sites onthe metal surface and thereby facilitate chemical bonding of the PTFE tothe substrate. Because polymeric materials such as PTFE are stable andquite non-reactive, additional energy may be required to induce thereactions that bond the material to the surface. Therefore, whendepositing polymeric materials, it may be beneficial to use highervelocity deposition parameters. However, higher velocities requirehigher gas flows and therefore it is instead preferred to use a largersize abrasive grit to provide additional kinetic energy. If abrasiveparticles greater than 1500 microns in size are used, then there areinsufficient impacts per unit area to bond the polymer to the surface.If small grit particles less than 150 microns in size are used, then theimpinging abrasive may lack the kinetic energy to induce reactions withthe non-reactive polymer material. When depositing polymeric materialsit is therefore preferred to use abrasive particles of 150 to 1500microns in size, preferably 250 to 1000 microns in size, and mostpreferably 350 to 750 microns in size as these possess higher kineticenergy and produce enhanced surface abrasion and roughening. However,nowithstanding the above, we have also achieved good deposition ofpolymer dopants using abrasive particles having an average particle sizeof the order of 50 microns or smaller, and, separately, using abrasiveparticles having an average particle size of the order of 13 microns orsmaller.

In addition, when depositing polymeric dopants, the blend of dopant andabrasive should be altered to be rich in abrasive. While standardblasting is carried out with equal mixtures by weight of dopant andabrasive, for polymer dopants it has been found that a ratio of at least60 wt % abrasive and a maximum of 40 wt % dopant is preferred. A morepreferred ratio comprises at least 70 wt % abrasive and no more than 30wt % dopant. In the most preferred ratio, the mixture comprises 80-90 wt% abrasive and 10-20 wt % dopant. At mixtures above around 90 wt % or 95wt % abrasive, there is limited polymer deposition due to excessabrasion, although mixtures having between 90 wt % and 95 wt % abrasivecan advantageously be used to produce (deliberately) a very thin dopantlayer.

Although using a high loading of abrasive in the mixed media and a highaverage particle size has been beneficial for polymeric dopants, thisdoes not hold true for other dopants. When attempting to depositceramics, salts, metals or other materials, it has been found that theparticle size of the abrasive is key to producing an optimal coating.While larger abrasive particles give rise to enhanced surface roughness,it has been found that the use of smaller abrasives can give rise tohigher surface loadings of dopant. As the loading of the surface isdriven by the impaction of the abrasive on the surface, it is preferredto bombard the surface with a large number of smaller particles ratherthan fewer large particles. This produces more impacts and more surfacereactions per unit surface area and thereby facilitates enhanced surfaceloading of dopant. While deposition of dopant materials can be achievedusing abrasives with an average particle size of 500-1000 microns, ithas been observed that better results occur with abrasive particles thatare less than 500 microns, preferably less than 200 microns, and ideallyin the range of 10-150 microns average particle size. In addition, fornon-polymeric dopants, the maximum ratio of abrasive to dopant has beenfound to be 80 wt % abrasive to 20 wt % dopant, with better loading ofthe dopant formed when the mixture contains no more than 75 wt %abrasive and at least 25 wt % dopant. The optimum surface loading ofnon-polymeric dopants is achieved when the mixture contains no more than60 wt % abrasive and greater than 40 wt % dopant. Although a range ofabrasive particles have been successfully employed in CoBlast, theaverage dopant particle is typically in the range of 1-100 microns insize.

A blend of abrasive sizes may also be used when depositing dopantparticles using the CoBlast process. For example, large abrasiveparticles may be used for surface profile and cleaning effects,simultaneously with small abrasive particles in order to achieve goodsurface coverage and improved reactivity. For these reasons, and by wayof example, we have successfully used a blend of approximately 600micron and approximately 50 micron alumina abrasive particles whendepositing epoxies, zinc phosphate and others as the dopant species.

In some cases where high surface profile is required it may be mostefficient to grit-blast first with large abrasive particles (e.g. havingan average particle size of the order of 1500 microns or greater), andthen subsequently employ a CoBlast process using small abrasiveparticles simultaneously with the dopant particles.

Smaller dopants are more reactive, but larger dopant particles areeasier to flow in a powder feeder and are therefore often preferred. Inorder to commercialise a coating process, the optimal coating may beproduced using smaller particles, but the requirement to flow theparticles in a smooth and continuous manner from one or more hoppers tothe/each delivery nozzle may require the addition of flow agents or theuse of larger abrasive or dopant particles. In order to ensure acontinuous flow of media from the/each hopper to the/each nozzle it hasbeen found that the mixture of abrasive and dopant should have a Hausnerratio of less than 1.2 (and particularly preferably less than 1.15). Formixtures with a Hausner ratio greater than this value but less thanaround 1.3-1.5, it is possible to flow the material from a pressure potas long as the powders are dry, sealed and the total load of powder doesnot exceed 1.5 kg. If the mixture has a Hausner ratio greater thanaround 1.3-1.5, then it is necessary to physically agitate the mixtureusing stirring rods, bars, blades or other devices to prevent the powderfrom compacting and to maintain a constant flow. If the Hausner ratioexceeds around 1.5-1.6, then the maximum load that can be fed from thehopper is 500 g in order to ensure that the powder does not compact andblock the system. For optimum performance, the hopper should be loadedwith no more than 400 g of mixed media. In order to ensure a constantsupply to the nozzle, it may be beneficial to employ multiple powderfeeders each loaded with small quantities of mixed media, preferablyless than 500 g.

The Hausner ratio values in the above paragraph are by way of exampleonly, in respect of a specific deposition system we use. For otherconfigurations of the apparatus the Hausner ratio values may differ.

The deposited CoBlast layer is typically limited to a thin deposit of2-5 microns, although thicker deposits of up to 10 microns are possible.When attempting to produce thicker deposits, the presence of theabrasive eventually begins to produce excess abrasion and thickercoatings are rapidly removed, meaning that the process is self-limitingwith a maximum thickness of 10 microns achievable. In order to depositthicker coatings, it is beneficial to first deposit a CoBlast layerusing a combination of dopant and abrasive. This produces a thin andchemically bonded primer layer onto which additional materials can thenbe deposited. In a preferred embodiment, the CoBlast process is used todeposit a thin layer of dopant on the surface. The flow of abrasive anddopant is then switched off or redirected and a second bombardment ofthe surface takes place. This second bombardment can be based on a coldspray process in which additional materials are blasted at the surfacewith the required critical velocity to adhere the particles to thesurface. The benefit of first employing the CoBlast process is that thisfacilitates the direct chemical bonding of the coating to the metalwithout an intervening oxide layer and thereby minimises the risk ofcoating delamination.

Alternatively, the second bombardment may be carried out using a mixtureof dopant particles and round shot peen particles. The switch fromangular abrasive grit to spherical shot peen particles ensures that thesecondary process is not dominated by abrasive erosion, and thickcoatings can be grown which are anchored to the metal surface by theCoBlast primer layer. This secondary bombardment can be carried outusing the same equipment as used in the CoBlast treatment or cancomprise a second set of equipment. In a third alternative, thesecondary bombardment may involve simply blasting a dopant, without anyadditional material, at the CoBlast treated surface so as to build up azo thicker coating, but without using the high temperatures or highvelocity of the cold spray process. This represents a microblast processsimilar to that described by Ishikawa. The dopant used in any of thesecondary bombardment steps may be identical to the dopant used in theCoBlast treatment or it may be different from the CoBlast dopantmaterials. In each case, the CoBlast layer will act to improve adhesionof the secondary coating by directly bonding the top coat to the metalwithout any oxide interface. In a preferred method, the top coating isthen further processed using thermal, laser, e-beam or some other highenergy method in order to cross-link, melt, densify or cure the coating.This also causes the top layer to fuse with the CoBlast primer layer,thereby chemically bonding the top coat directly to the metal substrate.

Instead of using a bombardment process, the secondary surface treatmentmay be added using traditional methods such as painting, sputtering,CVD, plasma deposition, ion plating, PVD, ion beam assisted deposition,electron beam PVD, cathodic arc deposition, magnetron sputtering, vacuumevaporation, laser assisted deposition, PECVD, electroplating, spraying,HVOF, powder coating, dip coating, inkjet printing, roller coating,lithography, spin coating or other such technologies. In each case, theinitial layer of dopant acts as a primer that allows the top coating tobe bound directly to the metal substrate without any intermediate oxidelayer. Further curing or heating of the top coat can enhance the bondingto the substrate further.

There are a wide variety of dopants that can be used in this process.The dopant can comprise materials such as polymers, metals, ceramics(e.g., metal oxides, metal nitrides), and combinations thereof, e.g.,blends of two or more thereof.

Exemplary dopants include modified calcium phosphates, includingCa₅(PO₄)₃OH, CaHPO₄·2H₂O, CaHPO₄, Ca₈H₂(PO₄)₆·5H₂O, α-Ca₃(PO₄)₂,β-Ca₃(PO₄)₂, tetracalcium phosphate, beta calcium phosphate or anymodified calcium phosphate containing carbonate, chloride, fluoride,silicate or aluminate anions, protons, potassium, sodium, magnesium,barium or strontium cations.

Other dopants include titania (TiO₂), hydroxyapatite, silica, calciumcarbonate, biocompatible glass, calcium phosphate glass, carbon,graphite, graphene, chitosan, chitin, barium titanate, zeolites(aluminosilicates), including siliceacous zeolite and zeolitescontaining at least one component selected from phosphorous, silica,alumina, zirconia.

In one embodiment, the dopant is a therapeutic agent. The therapeuticagent can be delivered as a particle itself, or immobilized on a carriermaterial. Exemplary carrier materials include any of the other dopantslisted herein (those dopants that are not a therapeutic agent) such aspolymers, calcium phosphate, titanium dioxide, silica, biopolymers,biocompatible glasses, zeolite, demineralized bone, de-proteinated bone,allograft bone, and composite combinations thereof.

Exemplary classes of therapeutic agents include anti-cancer drugs,anti-inflammatory drugs, immunosuppressants, an antibiotic, heparin, afunctional protein, a regulatory protein, structural proteins,oligo-peptides, antigenic peptides, nucleic acids, immunogens, andcombinations thereof.

In one embodiment, the therapeutic agent is chosen from antithrombotics,anticoagulants, antiplatelet agents, thrombolytics, antiproliferatives,anti-inflammatories, antimitotic, antimicrobial, agents that inhibitrestenosis, smooth muscle cell inhibitors, antibiotics, fibrinolytic,immunosuppressive, and anti-antigenic agents.

Exemplary anticancer drugs include acivicin, aclarubicin, acodazole,acronycine, adozelesin, alanosine, aldesleukin, allopurinol sodium,altretamine, aminoglutethimide, amonafide, ampligen, amsacrine,androgens, anguidine, aphidicolin glycinate, asaley, asparaginase,5-azacitidine, azathioprine, Bacillus calmette-guerin (BCG), Baker'sAntifol (soluble), beta-2′-deoxythioguanosine, bisantrene HCl, bleomycinsulfate, busulfan, buthionine sulfoximine, BWA 773U82, BW 502U83.HCl, BW7U85 mesylate, ceracemide, carbetimer, carboplatin, carmustine,chlorambucil, chloroquinoxaline-sulfonamide, chlorozotocin, chromomycinA3, cisplatin, cladribine, corticosteroids, Corynebacterium parvum,CPT-11, crisnatol, cyclocytidine, cyclophosphamide, cytarabine,cytembena, dabis maleate, dacarbazine, dactinomycin, daunorubicin HCl,deazauridine, dexrazoxane, dianhydrogalactitol, diaziquone,dibromodulcitol, didemnin B, diethyldithiocarbamate, diglycoaldehyde,dihydro-5-azacytidine, doxorubicin, echinomycin, edatrexate, edelfosine,eflornithine, Elliott's solution, elsamitrucin, epirubicin, esorubicin,estramustine phosphate, estrogens, etanidazole, ethiofos, etoposide,fadrazole, fazarabine, fenretinide, filgrastim, finasteride, flavoneacetic acid, floxuridine, fludarabine phosphate, 5-fluorouracil,Fluosol.RTM., flutamide, gallium nitrate, gemcitabine, goserelinacetate, hepsulfam, hexamethylene bisacetamide, homoharringtonine,hydrazine sulfate, 4-hydroxyandrostenedione, hydrozyurea, idarubicinHCl, ifosfamide, interferon alfa, interferon beta, interferon gamma,interleukin-1 alpha and beta, interleukin-3, interleukin-4,interleukin-6, 4-ipomeanol, iproplatin, isotretinoin, leucovorincalcium, leuprolide acetate, levamisole, liposomal daunorubicin,liposome encapsulated doxorubicin, lomustine, lonidamine, maytansine,mechlorethamine hydrochloride, melphalan, menogaril, merbarone,6-mercaptopurine, mesna, methanol extraction residue of Bacilluscalmette-guerin, methotrexate, N-methylformamide, mifepristone,mitoguazone, mitomycin-C, mitotane, mitoxantrone hydrochloride,monocyte/macrophage colony-stimulating factor, nabilone, nafoxidine,neocarzinostatin, octreotide acetate, ormaplatin, oxaliplatin,paclitaxel, pala, pentostatin, piperazinedione, pipobroman, pirarubicin,piritrexim, piroxantrone hydrochloride, PIXY-321, plicamycin, porfimersodium, prednimustine, procarbazine, progestins, pyrazofurin, razoxane,sargramostim, semustine, spirogermanium, spiromustine, streptonigrin,streptozocin, sulofenur, suramin sodium, tamoxifen, taxotere, tegafur,teniposide, terephthalamidine, teroxirone, thioguanine, thiotepa,thymidine injection, tiazofurin, topotecan, toremifene, tretinoin,trifluoperazine hydrochloride, trifluridine, trimetrexate, tumornecrosis factor, uracil mustard, vinblastine sulfate, vincristinesulfate, vindesine, vinorelbine, vinzolidine, Yoshi 864, zorubicin, andmixtures thereof.

Exemplary therapeutic agents include immunogens such as a viral antigen,a bacterial antigen, a fungal antigen, a parasitic antigen, tumorantigens, a peptide fragment of a tumor antigen, meta static specificantigens, a passive or active vaccine, a synthetic vaccine or a subunitvaccine. The dopant may be a protein such as an enzyme, antigen, growthfactor, hormone, cytokine or cell surface protein.

The dopant may be a pharmaceutical compound such as an anti-neoplasticagent, an anti-bacterial agent, an anti-parasitic agent, an anti-fungalagent, an analgesic agent, an anti-inflammatory agent, achemotherapeutic agent, an antibiotic or combinations thereof.

The dopant could also be growth factors, hormones, immunogens, proteinsor pharmaceutical compounds that are part of a drug delivery system suchas those immobilized on zeolite or polymeric matrices, biocompatibleglass or natural porous apitic templates such as coralline HA,demineralised bone, deproteinated bone, allograft bone, collagen orchitin.

In one embodiment, the dopant is an anti-inflammatory drug selected fromnon-steroidal anti-inflammatory drugs, COX-2 inhibitors,glucocorticoids, and mixtures thereof. Exemplary non-steroidalanti-inflammatory drugs include aspirin, diclofenac, indomethacin,sulindac, ketoprofen, flurbiprofen, ibuprofen, naproxen, piroxicam,tenoxicam, tolmetin, ketorolac, oxaprosin, mefenamic acid, fenoprofen,nambumetone, acetaminophen, and mixtures thereof. Exemplary COX-2inhibitors include nimesulide, NS-398, flosulid, L-745337, celecoxib,rofecoxib, SC-57666, DuP-697, parecoxib sodium, JTE-522, valdecoxib,SC-58125, etoricoxib, RS-57067, L-748780, L-761066, APHS, etodolac,meloxicam, S-2474, and mixtures thereof. Exemplary glucocorticoidsinclude hydrocortisone, cortisone, prednisone, prednisolone,methylprednisolone, meprednisone, triamcinolone, paramethasone,fluprednisolone, betamethasone, dexamethasone, fludrocortisone,desoxycorticosterone, and mixtures thereof.

Other exemplary therapeutic agents include cell cycle inhibitors ingeneral, apoptosis-inducing agents, antiproliferative/antimitotic agentsincluding natural products such as vinca alkaloids (e.g., vinblastine,vincristine, and vinorelbine), paclitaxel, colchicine,epidipodophyllotoxins (e.g., etoposide, teniposide), enzymes (e.g.,L-asparaginase, which systemically metabolizes L-asparagine and deprivescells that do not have the capacity to synthesize their own asparagine);antiplatelet agents such as G(GP) IIb/IIIa inhibitors, GP-IIa inhibitorsand vitronectin receptor antagonists; antiproliferative/antimitoticalkylating agents such as nitrogen mustards (mechlorethamine,cyclophosphamide and analogs, melphalan, chlorambucil), ethyleniminesand methylmelamines (hexamethylmelamine and thiotepa), alkylsulfonates-busulfan, nitrosoureas (carmustine (BCNU) and analogs,streptozocin), triazenes-dacarbazine (DTIC);antiproliferative/antimitotic antimetabolites such as folic acid analogs(methotrexate), pyrimidine analogs (fluorouracil, floxuridine, andcytarabine), purine analogs and related inhibitors (mercaptopurine,thioguanine, pentostatin and 2-chlorodeoxyadenosine (cladribine));platinum coordination complexes (cisplatin, carboplatin), procarbazine,hydroxyurea, mitotane, aminoglutethimide; hormones (e.g., estrogen);anticoagulants (heparin, synthetic heparin salts and other inhibitors ofthrombin); fibrinolytic agents (such as tissue plasminogen activator,streptokinase and urokinase), aspirin, dipyridamole, ticlopidine,clopidogrel, abciximab; antimigratory; antisecretory (breveldin);anti-inflammatory: such as adrenocortical steroids (cortisol, cortisone,fluorocortisone, prednisone, prednisolone, 6α-methylprednisolone,triamcinolone, betamethasone, and dexamethasone), non-steroidal agents(salicylic acid derivatives e.g., aspirin; para-aminophenol derivativese.g., acetominophen; indole and indene acetic acids (indomethacin,sulindac, and etodalac), heteroaryl acetic acids (tolmetin, diclofenac,and ketorolac), arylpropionic acids (ibuprofen and derivatives),anthranilic acids (mefenamic acid, and meclofenamic acid), enolic acids(piroxicam, tenoxicam, phenylbutazone, and oxyphenthatrazone),nabumetone, gold compounds (auranofin, aurothioglucose, gold sodiumthiomalate); immunosuppressives: (cyclosporine, tacrolimus (FK-506),sirolimus (rapamycin), azathioprine, mycophenolate mofetil); antigenicagents: vascular endothelial growth factor (VEGF), fibroblast growthfactor (FGF); angiotensin receptor blockers; nitric oxide donors;anti-sense oligionucleotides and combinations thereof; cell cycleinhibitors, mTOR inhibitors, and growth factor receptor signaltransduction kinase zo inhibitors; retinoid; cyclin/CDK inhibitors; HMGco-enzyme reductase inhibitors (statins); and protease inhibitors(matrix protease inhibitors).

In one embodiment, the dopant is an antibiotic chosen from tobramycin,vancomycin, gentamicin, ampicillin, penicillin, cephalosporin C,cephalexin, cefaclor, cefamandole and ciprofloxacin, dactinomycin,actinomycin D, daunorubicin, doxorubicin, idarubicin, penicillins,cephalosporins, and quinolones, anthracyclines, mitoxantrone,bleomycins, plicamycin (mithramycin), mitomycin, polyketide antibioticssuch as tetracycline, and mixtures thereof.

In one embodiment, the dopant is a protein chosen from albumin, casein,gelatin, lysosime, fibronectin, fibrin, chitosan, polylysine,polyalanine, polycysteine, Bone Morphogenetic Protein (BMP), EpidermalGrowth Factor (EGF), Fibroblast Growth Factor (bFGF), Nerve GrowthFactor (NGF), Bone Derived Growth Factor (BDGF), Transforming GrowthFactor-.beta.1 (TGF-.beta.1), Transforming Growth Factor-.beta.(TGF-.beta.), the tri-peptide arginine-glycine-aspartic acid (RGD),vitamin D3, dexamethasone, and human Growth Hormone (hGH), epidermalgrowth factors, transforming growth factor a, transforming growth factorβ, vaccinia growth factors, fibroblast growth factors, insulin-likegrowth factors, platelet derived growth factors, cartilage derivedgrowth factors, interlukin-2, nerve cell growth factors, hemopoieticcell growth factors, lymphocyte growth factors, bone morphogenicproteins, osteogenic factors, chondrogenic factors, and mixturesthereof.

In one embodiment, the dopant is a heparin selected from recombinantheparin, heparin derivatives, and heparin analogues or combinationsthereof. In one embodiment, the dopant is an oligo-peptide, such as abactericidal oligo-peptide. In one embodiment, the dopant is anosteoconductive or osteointegrative agent.

In one embodiment, the dopant is an immunosuppressant, such ascyclosporine, rapamycin and tacrolimus (FK-506), ZoMaxx, everolimus,etoposide, mitoxantrone, azathioprine, basiliximab, daclizumab,leflunomide, lymphocyte immune globulin, methotrexate, muromonab-CD3,mycophenolate, and thalidomide.

In one embodiment, the carrier material is a polymer such aspolyurethanes, polyethylene terephthalate, PLLA-poly-glycolic acid (PGA)copolymer (PLGA), polycaprolactone,poly-(hydroxybutyrate/hydroxyvalerate) copolymer,poly(vinylpyrrolidone), polytetrafluoroethylene,poly(2-hydroxyethylmethacrylate), poly(etherurethane urea), silicones,acrylics, epoxides, polyesters, urethanes, parlenes, polyphosphazenepolymers, fluoropolymers, polyamides, polyolefins, and blends andcopolymers thereof.

In one embodiment, the carrier material is a biopolymer selected frompolysaccharides, gelatin, collagen, alginate, hyaluronic acid, alginicacid, carrageenan, chondroitin, pectin, chitosan, and derivatives,blends and copolymers thereof.

In one embodiment, the dopant is a radio opaque material, such as thosechosen from alkalis earth metals, transition metals, rare earth metals,and oxides, sulphates, phosphates, polymers and combinations thereof.

In one embodiment, the dopant is a pigment designed to alter theemission, absorbance or reflectance of a surface. The deposited pigmentmay comprise part of a thermal control surface.

In one embodiment, the surface containing the deposited dopant may beelectrically conductive. This conductivity may be sufficient to preventthe build-up of electrical static charge on the surface.

In one embodiment, the dopant is a component present within an adhesiveor paint. This component may bind to the adhesive or paint as it curesthereby chemically bonding the top layer to the substrate. Examples ofsuch components include monomers, pre-polymers, pigments, silanes,fillers such as silica or clay . The dopant may be fusion bonded epoxy,including of derivatives of bisphenol A and epichlorohydrin. The dopantmay be an epoxy prepolymer or may be derived zo from bisphenol A,bisphenol F, Novolac, Glycidylamine epoxy resins or aliphatic epoxyresin. The component may be an additive such as accelerators, corrosioninhibitors, adhesion promoters, fire retardants or fungicides. Typicalcorrosion-inhibiting dopant species that may be used in the presentmethod include but are not limited to a chromate, phosphate, polymer,oxide or a nitride. For example, the dopant may be ceria. In a preferredmethod, the coating is derived from a phosphate compound. The phosphatemay comprise iron phosphate, manganese phosphate, zinc phosphate orcombinations thereof. Alternatively, or in addition, a primer-formingdopant species may comprise a silane, siloxane, acrylate, epoxy,hydrogen bonded silicon compound or material which contains one or morevinyl, peroxyester, peroxide, acetate or carboxylate functional group.

Abrasive species that may be used in the present method (as a second setof particles, delivered substantially simultaneously with the first)include but are not limited to shot or grit made from silica, sand,alumina, zirconia, barium titanate, calcium titanate, sodium titanate,titanium oxide, glass, biocompatible glass, diamond, silicon carbide,boron carbide, dry ice, boron nitride, sintered calcium phosphate,calcium carbonate, metallic powders, carbon fibre composites, polymericcomposites, titanium, stainless steel, hardened steel, carbon steelchromium alloys or any combination thereof. The abrasive is chosen to bea different material than the dopant.

Examples of substrates that may be treated using this technology includemetals and intermetallic compounds, such as those metals chosen frompure metals, metal alloys, intermetallics comprising single or multiplephases, intermetallics comprising amorphous phases, intermetallicscomprising single crystal phases, and intermetallics comprisingpolycrystalline phases. Exemplary metals include titanium, titaniumalloys (e.g., NiTi or nitinol), ferrous alloys, stainless steel andstainless steel alloys, carbon steel, carbon steel alloys, aluminum,aluminum alloys, nickel, nickel alloys, nickel titanium alloys,tantalum, tantalum alloys, niobium, niobium alloys, chromium, chromiumalloys, cobalt, cobalt alloys, magnesium and magnesium alloys, copperand copper alloys, precious metals, and precious metal alloys.

In one embodiment, the substrate is an implantable medical device.Exemplary medical devices include catheters, guide wires, stents, dentalimplants, pulse generators, implantable orthopedic, spinal andmaxillofacial devices, cochlear implant, needles, mechanical heartvalves and baskets used in the removal of pathological calcifications.In the case of biomedical devices it is desirable that the level ofimpregnation of the abrasive itself in the surface is minimal. Theabrasive should further be biocompatible as it is likely that someimpregnation will occur.

In one embodiment, the substrate is a vehicle component, including anautomotive chassis, body or panel component, or an aerospace vehicle,satellite, rocket or spacecraft component, or a marine ship or boatcomponent, specifically the outer hull. In one embodiment, the substrateis an engine or an engine component including exhaust outlets.

The substrate may be an electronic component, including components foruse in applications in the Communication Infrastructure, Aerospace andDefence, Automotive, Mobile and Consumer Electronics, and High SpeedDigital markets. The electronic components may include circuit boards,cases, housing, switches, terminals, protection devices, transducers,capacitors, resistors, heat exchangers, antennas, human interfaces,dielectrics, thermal control surfaces, power sources or displaycomponents.

In one embodiment, the substrate is a mould such as that used in themanufacture of plastic, silicone, rubber, composite, polymer, clay,glass, metal or ceramic materials. The dopant may be chosen to enhancerelease of the cast part from the mould and the dopant may comprise afluoropolymer or silicone material.

In one embodiment the substrate may be a pipe, tube or storage vessel,specifically one used in the petrochemical, marine, pharmaceutical,chemical, biotech or food and beverage industry. The deposited dopantmay be chosen to zo minimise fouling or build-up of materials on theinside of the container.

The dopant and abrasive are preferentially mixed together and blasted ata surface. The blasting may be carried out using wheel abradingequipment or fluid based blast equipment. Where fluid blasting iscarried out, the fluid may be a gas or a liquid, such as water.Appropriate gases include air, nitrogen, argon, helium, carbon dioxideor mixtures thereof. If using combustible or explosive media, the fluidmay comprise water or may be largely composed of an inert gas.

Example 1

An aluminium sample was electrolytically plated to produce a uniform 12micron thick metallic Ni layer. This surface was then subjected to aCoBlast surface treatment using alumina as the abrasive and calciumphosphate as the dopant. The powders were pre-mixed and blasted at thesurface. As can be seen from the optical micrographs in FIG. 4 and theEDX analysis in FIG. 5, following the CoBlast treatment the nickel wasstill evident on the surface of the substrate, indicating that there wasless than 12 microns eroded from the substrate surface. In addition, theEDX shows the presence of additional elements attributed to the presenceof the calcium phosphate dopant impregnated into the surface. Closeexamination of the optical micrographs in FIG. 4 shows that all of thenickel plating is not removed during the CoBlast treatment. However, itcan be seen that there is some level of nickel removal from the surfaceduring CoBlast, based on the cross-sectional analysis. Although theremoval rate is not uniform, there is typically 2-10 microns of metalremoved. The overall thickness of the substrate does not altersignificantly as any metal removal is offset by deposition of the dopantmaterial. It is also clear that the CoBlast treated surface is rougherthan the untreated nickel surface.

Example 2

150 micron alumina abrasive was mixed with calcium phosphate(Hydroxyapatite or HA, 20-65 micron average particle size) and blastedat a series of grade 2 titanium coupons. The velocity of the bombardingparticle was varied from 170-195 m/sec. Samples were then washed andexamined using SEM. In each case, the surface was found to be loadedwith high levels of calcium and phosphorous, confirming that calciumphosphate had been deposited in each case. Samples were also subjectedto XRD analysis. In each case, the analysis detected only peaksassociated with titanium and the calcium phosphate deposit. Analysis ofthe ratio of the intensity of the HA (211) peak to the intensity of theTi (101) peak showed approximately equivalent signals for all samples.

The adhesion of the deposited material was measured using a test methodbased on ASTM F1147. This determined that the adhesion of the depositwas in excess of 58 MPa, which was the failure point of the adhesive.

This experiment was then repeated, but instead of using angular aluminaabrasive, the calcium phosphate was mixed with round shot peeningparticles made from grade 5 titanium. Initial SEM analysis detectedcalcium phosphate on the surface, though there appeared to besignificantly less material present. This was confirmed by XRD analysis.A comparison of the ratio of the intensity of the HA (211) peak to theintensity of the Ti (101) peak showed significant differences from theresult achieved using the alumina abrasive. The Ti peak wassignificantly more pronounced in the spectra derived from the shot peensamples and was found to be 3-4 times more intense than the HA peak,confirming that significantly less calcium phosphate material wasdeposited using the spherical shot peen media.

The maximum adhesion measured for the shot peen samples was alsomeasured and an average value of 25 MPa was recorded. This issignificantly below the level measured for the samples deposited usingan abrasive, thereby confirming that the samples produced by abrasiveblasting had a much stronger adhesive bond to the substrate, as would beexpected from a chemically bonded material.

This data confirms that deposition of a ceramic dopant using abrasivemedia can be accomplished at lower velocities than are used in coldspray processes and that the shape of the bombarding particle is key.Rough, irregular shaped abrasive particles can assist with thedeposition of a dopant in far higher loadings zo than can be achievedwith a spherical shot peen bombardment particle. Furthermore, theabrasive particles enhance the adhesion of the dopant to the substrate.

Example 3

A series of 1 mm thick Grade 5 titanium samples were subjected toabrasive bombardment using a 50:50 mixture of 100 micron aluminaabrasive and hydroxyapatite (25-60 microns particle distribution) and abombardment height of 41 mm. Particle image velocimetry (PIV) was usedto quantify the velocity of the bombarding particles. The samples weresubject to bombardment at various particle velocities and the surface ofthe blasted substrates was then subjected to 5 minutes cleaning in anultrasonic bath filled with deionised water. The samples were air driedand then analysed using SEM-EDX. Signals arising from lighter elementsuch as carbon and oxygen were not measured and instead the analysisfocussed on the heavier elements of Ca, P and Ti.

At velocities less than 100 m/sec, there was minimal hydroxyapatitedetected on the surface of the titanium coupons. At velocities in excessof 100 m/sec, there was significant hydroxyapatite loading of the metal.Samples blasted at a velocity of 115 m/sec had an average loading ofcalcium+phosphorous of 29%, with the remained of the material comprisingtitanium. SEM imaging detected significant loading of material on thesurface. Increasing the velocity further to 194 m/sec resulted insignificantly higher loading of 46% calcium+phosphorous, with theremainder comprising titanium.

Example 4

Polytetrafluoroethylene (PTFE) was deposited onto a superelastic NiTiwire at ambient temperature using <50 μm and <90 μm alumina with a blendratio of 50:50 by mass. The CoBlast coated wires were compared to wiretreated with PTFE only. The coated samples were examined using a varietyof techniques: microscopy, surface roughness, wear testing and flexuraltests, for which the results are shown in FIG. 6. It can be seen thatthe CoBlast coated samples zo (samples (b) and (c) in FIG. 6) had anadherent coating with a significant resistance to wear compared to thesamples coated with PTFE only (sample (a) in FIG. 6). This studyindicates that the CoBlast process can successfully be used to depositthin adherent coatings of PTFE onto the surface of superelastic NiTi.

1. A metal surface treatment method wherein the surface issimultaneously bombarded with a mixture of abrasive particles and dopantparticles which are delivered at a velocity in the range of 50-250m/sec, and thereby depositing the dopant material on the surface.
 2. Amethod as claimed in claim 1, wherein the particles are delivered at avelocity in the range of 100-200 m/sec.
 3. A method as claimed in claim2, wherein the particles are delivered at a velocity in the range of120-180 m/sec.
 4. A method as claimed in claim 1, carried out at ambienttemperature.
 5. A method as claimed in claim 1, wherein the abrasiveparticles have an irregular or angular morphology.
 6. A method asclaimed in claim 1, wherein the dopant is directly chemically bonded tothe metal surface without any intermediate oxide layer.
 7. A method asclaimed in claim 1, wherein the dopant particles are agglomeratedtogether on the metal surface.
 8. A method as claimed in claim 1,wherein the abrasive has a hardness greater than 6.0 on the Mohs scale.9. A method as claimed in claim 1, wherein the abrasive has a hardnessof 8.0 or above on the Mohs scale.
 10. A method as claimed in claim 1,wherein the abrasive has a hardness at least 2 levels higher than thatof the dopant on the Mohs scale.
 11. (canceled)
 12. A method as claimedin claim 1, wherein the dopant is a polymer and the abrasive has anaverage particle size in the range of 5-5000 microns.
 13. A method asclaimed in claim 12, wherein the abrasive has an average particle sizein the range of 5-1500 microns. 14-17. (canceled)
 18. A method asclaimed in claim 1, wherein the dopant is a polymer and the abrasive hasan average particle size of greater than 300 microns.
 19. A method asclaimed in claim 1, wherein the abrasive constitutes at least 60 wt % ofthe mixture of abrasive and dopant particles. 20-21. (canceled)
 22. Amethod as claimed in claim 1, wherein the dopant is a non-polymericmaterial and the abrasive has an average particle size of less than 500microns. 23-24. (canceled)
 25. A method as claimed in claim 22, whereinthe dopant constitutes at least 20 wt % of the mixture of abrasive anddopant particles. 26-27. (canceled)
 28. A method as claimed in claim 1,wherein the dopant particles have an average particle size in the rangeof 1-100 microns.
 29. (canceled)
 30. A method as claimed in claim 1,wherein at least some of the dopant particles penetrate the metalsurface and remain physically impregnated in the metal.
 31. A method asclaimed in claim 1, further comprising applying an additional coating ontop of the deposited dopant material.
 32. A method as claimed in claim31, wherein the additional coating is applied through a bombardmenttechnique selected from cold spray, peen plating or microblasting.33-36. (canceled)